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All of the blood cells in your body - white blood cells, red blood cells, and platelets - start out as young (immature) cells called hematopoietic stem cells. Hematopoietic means blood-forming. These are very young cells that are not fully developed. Even though they start out the same, these stem cells can mature into any type of blood cell, depending on what the body needs when each stem cell is developing.
Stem cells mostly live in the bone marrow (the spongy center of certain bones). This is where they divide to make new blood cells. Once blood cells mature, they leave the bone marrow and enter the bloodstream. A small number of the immature stem cells also get into the bloodstream. These are called peripheral blood stem cells.
Stem cells make red blood cells, white blood cells, and platelets. We need all of these types of blood cells to keep us alive. For these blood cells to do their jobs, you need to have enough of each of them in your blood.
Red blood cells carry oxygen away from the lungs to all of the cells in the body. They bring carbon dioxide from the cells back to the lungs to be exhaled. A blood test called a hematocrit shows how much of your blood is made up of RBCs. The normal range is about 35% to 50% for adults. People whose hematocrit is below this level have anemia. This can make them look pale and feel weak, tired, and short of breath.
White blood cells help fight infections caused by bacteria, viruses, and fungi. There are different types of WBCs.
Neutrophils are the most important type in fighting infections. They are the first cells to respond to an injury or when germs enter the body. When they are low, you have a higher risk of infection. The absolute neutrophil count (ANC) is a measure of the number of neutrophils in your blood. When your ANC drops below a certain level, you have neutropenia. The lower the ANC, the greater the risk for infection.
Lymphocytes are another type of white blood cell. There are different kinds of lymphocytes, such as T lymphocytes (T cells), B lymphocytes (B cells), and natural killer (NK) cells. Some lymphocytes make antibodies to help fight infections. The body depends on lymphocytes to recognize its own cells and reject cells that don’t belong in the body, such as invading germs or cells that are transplanted from someone else.
Platelets are pieces of cells that seal damaged blood vessels and help blood to clot, both of which are important in stopping bleeding. A normal platelet count is usually between 150,000/cubic mm and 450,000/cubic mm, depending on the lab that does the test. A person whose platelet count drops below normal is said to have thrombocytopenia, and may bruise more easily, bleed longer, and have nosebleeds or bleeding gums. Spontaneous bleeding (bleeding with no known injury) can happen if a person’s platelet count drops lower than 20,000/mm3. This can be dangerous if bleeding occurs in the brain, or if blood begins to leak into the intestines or stomach.
You can get more information on blood counts and what the numbers mean in Understanding Your Lab Test Results.
Depending on the type of transplant that’s being done, there are 3 possible sources of stem cells to use for transplants:
Bone marrow is the spongy liquid tissue in the center of some bones. It has a rich supply of stem cells, and its main job is to make blood cells that circulate in your body. The bones of the pelvis (hip) have the most marrow and contain large numbers of stem cells. For this reason, cells from the pelvic bone are used most often for a bone marrow transplant. Enough marrow must be removed to collect a large number of healthy stem cells.
The bone marrow is harvested (removed) while the donor is under general anesthesia (drugs are used to put the patient into a deep sleep so they don’t feel pain). A large needle is put through the skin on the lower back and into the back of the hip bone. The thick liquid marrow is pulled out through the needle. This is repeated until enough marrow has been taken out. (For more on this, see What’s It Like to Donate Stem Cells?)
The harvested marrow is filtered, stored in a special solution in bags, and then frozen. When the marrow is to be used, it’s thawed and then put into the patient’s blood through a vein, just like a blood transfusion. The stem cells travel to the bone marrow, where they engraft or “take” and start to make blood cells. Signs of the new blood cells usually can be measured in the patient’s blood tests in a few weeks.
Normally, not many stem cells are found in the blood. But giving stem cell donors shots of hormone-like substances called growth factors a few days before the harvest makes their stem cells grow faster and move from the bone marrow into the blood.
For a peripheral blood stem cell transplant, the stem cells are taken from blood. A special thin flexible tube (called a catheter) is put into a large vein in the donor and attached to tubing that carries the blood to a special machine. The machine separates the stem cells from the rest of the blood, which is returned to the donor during the same procedure. This takes several hours, and may need to be repeated for a few days to get enough stem cells. The stem cells are filtered, stored in bags, and frozen until the patient is ready for them. (For more on this, see What’s It Like to Donate Stem Cells?)
When they’re given to the patient, the stem cells are put into a vein, much like a blood transfusion. The stem cells travel to the bone marrow, engraft, and then start making new, normal blood cells. The new cells are usually found in the patient’s blood in about 4 weeks.
The blood of newborn babies normally has large numbers of stem cells. After birth, the blood that’s left behind in the placenta and umbilical cord (known as cord blood) can be taken and stored for later use in a stem cell transplant. Cord blood can be frozen until needed. A cord blood transplant uses blood that normally is thrown out after a baby is born. After the baby is born, specially trained members of the health care team make sure the cord blood is carefully collected. The baby is not harmed in any way. More information on donating cord blood can be found in What’s It Like to Donate Stem Cells?
Even though the blood of newborns has large numbers of stem cells, cord blood is only a small part of that number. So, a possible drawback of cord blood is the smaller number of stem cells in it. But this is partly balanced by the fact that each cord blood stem cell can form more blood cells than a stem cell from adult bone marrow. Still, cord blood transplants can take longer to take hold and start working. Cord blood is given into the patient’s blood just like a blood transfusion.
Some cancers start in the bone marrow and others can spread to it. Cancer attacks the bone marrow, causing it to make too many of some cells that crowd out others, or causing it to make cells that aren’t healthy and don't work like they should. For these cancers to stop growing, they need bone marrow cells to work properly and start making new, healthy cells.
Most of the cancers that affect bone marrow function are leukemias, multiple myeloma, and lymphomas. All of these cancers start in blood cells. Other cancers can spread to the bone marrow, which can affect how blood cells function, too.
For certain types of leukemia, lymphoma, and multiple myeloma, a stem cell transplant can be an important part of treatment. The goal of the transplant is to wipe out the cancer cells and the damaged or non-healthy cells that aren't working right, and give the patient new, healthy stem cells to “start over."
Stem cell transplants are used to replace bone marrow cells that have been destroyed by cancer or destroyed by the chemo and/or radiation used to treat the cancer.
There are different kinds of stem cell transplants. They all use very high doses of chemo (sometimes along with radiation) to kill cancer cells. But the high doses can also kill all the stem cells a person has and can cause the bone marrow to completely stop making blood cells for a period of time. In other words, all of a person's original stem cells are destroyed on purpose. But since our bodies need blood cells to function, this is where stem cell transplants come in. The transplanted stem cells help to "rescue" the bone marrow by replacing the body’s stem cells that have been destroyed by treatment. So, transplanting the healthy cells lets doctors use much higher doses of chemo to try to kill all of the cancer cells, and the transplanted stem cells can grow into healthy, mature blood cells that work normally and reproduce cells that are free of cancer.
There's another way a stem cell transplant can work, if it's a transplant that uses stem cells from another person (not the cancer patient). In these cases, the transplant can help treat certain types of cancer in a way other than just replacing stem cells. Donated cells can often find and kill cancer cells better than the immune cells of the person who had the cancer ever could. This is called the “graft-versus-cancer” or “graft-versus-leukemia” effect. The "graft" is the donated cells. The effect means that certain kinds of transplants actually help kill off the cancer cells, along with rescuing bone marrow and allowing normal blood cells to develop from the stem cells.
Although a stem cell transplant can help some patients, even giving some people a chance for a cure, the decision to have a transplant isn’t easy. Like everything in your medical care, you need to be the one who makes the final choice about whether or not you’ll have a stem cell transplant. Transplant has been used to cure thousands of people with otherwise deadly cancers. Still, there are possible risks and complications that can threaten life, too. People have died from complications of stem cell transplant. The expected risks and benefits must be weighed carefully before transplant.
Your cancer care team will compare the risks linked with the cancer itself to the risks of the transplant. They may also talk to you about other treatment options or clinical trials. The stage of the cancer, patient’s age, time from diagnosis to transplant, donor type, and the patient’s overall health are all part of weighing the pros and cons before making this decision.
Here are some questions you might want to ask. For some of these, you may need to talk to the transplant team or the people who work with insurance and payments for the doctor’s office and/or the hospital:
Be sure to express all your concerns and get answers you understand. Make sure the team knows what’s important to you, too. Transplant is a complicated process. Find out as much as you can and plan ahead before you start.
It’s important to know the success rate of the planned transplant based on your diagnosis and stage in treatment, along with any other conditions that might affect you and your transplant. In general, transplants tend to work better if they’re done in early stages of disease or when you’re in remission, when your overall health is good. Ask about these factors and how they affect the expected outcomes of your transplant or other treatment.
Many people get a second opinion before they decide to have a stem cell transplant. You may want to talk to your doctor about this, too. Also, call your health insurance company to ask if they will pay for a second opinion before you go. You might also want to talk with them about your possible transplant, and ask which transplant centers are covered by your insurance.
Stem cell transplants cost a lot, and some types cost more than others. For example, getting a donor's cells costs more than collecting your own cells. And, different drug and radiation treatments used to destroy bone marrow can have high costs. Some transplants require more time in the hospital than others, and this can affect cost. Even though there are differences, stem cell transplants can cost hundreds of thousands of dollars.
A transplant (or certain types of transplants) is still considered experimental for some types of cancer, especially some solid tumor cancers, so insurers might not cover the cost.
No matter what illness you have, it’s important to find out what your insurer will cover before deciding on a transplant, including donor match testing, cell collection, drug treatments, hospital stay, and follow-up care. Go over your transplant plan with them to find out what’s covered. Ask if the doctors and transplant team you plan to use are in their network, and how reimbursement will work. Some larger insurance companies have transplant case managers. If not, you might ask to speak with a patient advocate. You can also talk with financial or insurance specialists at your doctor’s office, transplant center, and hospital about what expenses you are likely to have. This will help you get an idea of what you might have to pay in co-pays and/or co-insurance.
The National Foundation for Transplants (NFT) provides fund raising guidance to help patients, their families, and friends raise money for all types of stem cell transplants in the US. They can be reached online at www.transplants.org, or call 1-800-489-3863.
The American Cancer Society medical and editorial content team
Our team is made up of doctors and oncology certified nurses with deep knowledge of cancer care as well as journalists, editors, and translators with extensive experience in medical writing.
American Society of Clinical Oncology (ASCO). What is a stem cell transplant (bone marrow transplant)? 2018. Accessed at https://www.cancer.net/navigating-cancer-care/how-cancer-treated/bone-marrowstem-cell-transplantation/what-bone-marrow-transplant-stem-cell-transplant on March 17, 2020.
Im A, Pavletic SZ. Hematopoietic stem cell transplantation. In Niederhuber JE, Armitage JO, Kastan MB, Doroshow JH, Tepper JE, eds. Abeloff’s Clinical Oncology. 6th ed. Philadelphia, PA: Elsevier; 2020:461-469.
National Institutes of Health (NIH). Stem cell basics. 2016. Access at https://stemcells.nih.gov/info/basics.htm on March 17, 2020.
Last Revised: March 20, 2020
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